This invention concerns a process for making certain anti-inflammatory compounds. In particular, the application concerns a process for making compounds of formula I as disclosed hereinunder, which compounds are potent cyclooxygenase-2 inhibitors.
Non-steroidal, antiinflammatory drugs exert most of their antiinflammatory, analgesic and antipyretic activity and inhibit hormone-induced uterine contractions and certain types of cancer growth through inhibition of prostaglandin G/H synthase, also known as cyclooxygenase. Up until recently, only one form of cyclooxygenase had been characterized, this corresponding to cyclooxygenase-1 or the constitutive enzyme, as originally identified in bovine seminal vesicles. Recently the gene for a second inducible form of cyclooxygenase (cyclooxygenase-2) has been cloned, sequenced and characterized from chicken, murine and human sources. This enzyme is distinct from the cyclooxygenase-1 which has now also been cloned, sequenced and characterized from sheep, murine and human sources. The second form of cyclooxygenase, cyclooxygenase-2, is rapidly and readily inducible by a number of agents including mitogens, endotoxin, hormones, cytokines and growth factors. As prostaglandins have both physiological and pathological roles, we have concluded that the constitutive enzyme, cyclooxygenase-1, is responsible, in large part, for endogenous basal release of prostaglandins and hence is important in their physiological functions such as the maintenance of gastrointestinal integrity and renal blood flow. In contrast, we have concluded that the inducible form, cyclooxygenase-2, is mainly responsible for the pathological effects of prostaglandins where rapid induction of the enzyme would occur in response to such agents as inflammatory agents, hormones, growth factors, and cytokines. Thus, a selective inhibitor of cyclooxygenase-2 will have similar antiinflammatory, antipyretic and analgesic properties to a conventional non-steroidal antiinflammatory drug, and in addition would inhibit hormone-induced uterine contractions and have potential anti-cancer effects, but will have a diminished ability to induce some of the mechanism-based side effects. In particular, such a compound should have a reduced potential for gastrointestinal toxicity, a reduced potential for renal side effects, a reduced effect on bleeding times and possibly a lessened ability to induce asthma attacks in aspirin-sensitive asthmatic subjects.
WO 96/24585 published Aug. 15, 1996 and WO 96/10012, published Apr. 4, 1996 disclose methods of making 2-aryl-3-aryl-pyridines. See also EP-a-0 548 559; R. P. Thummel et al., Journal of Organic Chemistry, vo. 42, no. 16, 1977, pp. 2742-2447; Chemical and Pharmaceutical Bulletin, vol. 24, no. 1, 1976; DE 36 34 259 a; and EP-a-0 075 727. In the invention as disclosed hereinunder, 2-aryl-3-aryl-pyridines are prepared in a simple to conduct, 2 step conversion of a Weinreb amide to the penultimate ketosulfone from readily available starting materials. It is, therefore, surprisingly convenient and more efficient than the prevoiusly described procedure, in which the 2-aryl-3-aryl pyridine was constructed by serial stepwise addition of the aryl groups to the central pyridine ring. Moreover, the process of the instant invention is also surprisingly superior in that expensive palladium reagents are not required nor is the cumbersome protection/de-protection sequense of the prior art process.